Known electronic cameras include an image sensor which comprises a plurality of light sensitive elements or pixels which are arranged in rows and columns and which convert light incident through a lens of the camera into electrical signals. For the reading out of an image, each of the pixels is addressed and a signal which is proportional to a charge of the pixel collected by an exposure is directed to an output of the image sensor.
In cameras which simultaneously have a high number of light sensitive elements and a high frame rate, image sensors are used which have a plurality of outputs which can be read out in parallel—and thus faster—in a respective readout cycle. In addition, the columns can be divided into column groups which each have a plurality of columns, with the number of the columns in each of the column groups corresponding to the number of the outputs.
In this connection, the rows are associated with the outputs of the image sensor in the manner of unit matrices disposed next to one another so that the columns with the numbers n, n+a, n+2a, etc. are each associated with the output with the number n, with the columns and the outputs each being numbered continuously.
With an image sensor with 32 outputs and with a division of the columns into column groups, for example, in a first readout cycle, the 1st column of the image sensor which corresponds to the 1st column of the 1st column group is thus associated with the 1st output. The 2nd column of the image sensor which corresponds to the 2nd column of the 1st column group is associated with the 2nd output, etc. up to the 32nd column of the image sensor which corresponds to the 32nd column of the 1st column group which is associated with the 32nd output. In the following readout cycle, the 33rd column of the image sensor which corresponds to the 1st column of the 2n column group is again associated with the 1st output; the 34th column of the image sensor which corresponds to the 2nd column of the 2nd column group is again associated with the 2nd output, etc.
Each of the outputs of the image sensor has its own output amplifier, with the signals of the pixels being amplified by the output amplifier in order subsequently to be digitized. The signals are applied to the output amplifiers as analog electrical voltages which correspond to the collected charges.
The reading out of such an image sensor usually takes place row-wise, i.e. row for row. Within the respectively selected line, the signals of the associated pixels are switched to the outputs of the image sensor via corresponding control signals column-wise, i.e. column for column, or optionally column-group-wise, i.e. column group for column group, with the readout starting at a 1st column or column group located at an edge of the image sensor and being continued in increasing order with the respective directly adjacent column or column group, i.e. according to the arrangement order of the columns or column groups. It follows from this that the signals of the pixels of the 1st, 33rd, 65th, etc. column of the image sensor are output sequentially at the 1st output or at the 1st output amplifier respectively, that the signals of the pixels of the 2nd, 34th, 66th, etc. column of the image sensor are output at the 2nd output or 2nd output amplifier respectively, etc.
A strictly regular order is thus provided with known image sensors in which the signals of the pixels are switched to the output amplifier.
It is known that the respective signal currently applied at an output amplifier always includes a small portion, disposed in the per thousandth range, of the signal directly amplified beforehand by the respective output amplifier, said portion being caused, for example, by thermal effects and/or feedback effects on the power supply. Suitable circuits and calculation methods are known to counter the disturbing influence of the signal of the predecessor pixel. A complete compensation is, however, not possible.
If the image sensor only has one single output, and thus only one output amplifier, the signals of all the pixels are amplified by the same output amplifier, with the signals of pixels arranged directly next to one another being amplified directly sequentially such that the portion of the signal of the respective predecessor pixel is effective in the signal of the pixel arranged directly adjacent to the respective predecessor pixel. This admittedly generates a kind of blur in the image with large difference between two signals amplified directly after one another. However, this is not perceivable by the eye.
If the image sensor, however, has a plurality of outputs, as has been explained by way of example above, the portion of the signal of the respective predecessor pixel—that is the portion of the signal amplified directly beforehand—makes itself noticeable in the amplification of the signal of that pixel which is arranged remote from the predecessor pixel by the number of outputs. The signals of the pixels arranged between the predecessor pixel and the pixel remote from the predecessor pixel by the number of outputs are namely amplified by the output amplifiers of the other outputs. For example, in an image which shows a bright candle flame in an otherwise dark room, a visual echo of the candle flame is generated which is laterally offset from the original candle flame. Such an image interference is called a ghost image. In the example chosen, the ghost image is particularly easily visible since the echo occurs in a dark region. For example, with an image sensor having 32 outputs, the echo is offset from the original by 32 pixels.